Interpretive Summary: The use of Indian ricegrass as a revegetation species on western rangelands has been limited by its typically high levels of seed dormancy. Natural populations of this species often exhibit genetically controlled seed polymorphism, i.e., different morphs on different plants, and the different seed morphs at a site often differ in seed dormancy. Because the 'jumbo' seed morph is especially high in seed dormancy, we wished to evaluate the genetic relationships among jumbo morphs and more highly germinable non-jumbo morphs collected at the same and different sites. We used RAPD DNA markers to measure genetic distance among 18 jumbo morphs from different locations and 11 non-jumbo morphs from 9 of those locations. The jumbo morphs clustered into one of four clusters based on their geographical origin, two from the Intermountain Region and one from the Rocky Mountain Region. Because jumbo and non-jumbo morphs found at a single location typically clustered apart, we infer that local polymorphic populations represent overlapping waves of migration from different directions. Such knowledge is useful 1) to suggest where particular morphs might be adapted for revegetation purposes and 2) to determine which materials are most appropriate for release relative to what is already available.

Technical Abstract:
Indian ricegrass (Achnatherum hymenoides [Roem. & Schult.] Barkworth) is a rangeland species native to western North America that exhibits between-plant seed polymorphism associated with seed dormancy. We compared RAPD profiles of the relatively infrequent and highly dormant jumbo morph to its more germinable non-jumbo companion morphs, collected at 9 sites where they were sympatric. Jumbo accessions from 9 additional nonpolymorphic sites were included to better sample this morph across geographic space. In only one of 9 polymorphic sites examined did we find sympatric morphs to be fairly closely related, yet even in this exception RAPD profiles were quite distinct, suggesting a breeding system that is highly autogamous but which exhibits occasional hybridization. All 18 jubmo morphs and 7 of 11 non-jumbo morphs in the study grouped either in two major clusters corresponding to the Intermountain Region west of the continental divide (10 jumbo + 4 non-jumbo and 3 jumbo + 2 non-jumbo) or a third cluster corresponding to the Rocky Mountain Region east of the continental divide (5 jumbo + 1 non-jumbo). With one exception, sympatric morphs corresponded to separate clusters, suggesting that these local polymorphic populations represent overlapping waves of migration from different directions, possibly emigration from separate glacial refugia. The jumbo morphs exhibited moderate correlation between genetic distance and geographic distance, but the non-jumbo morphs exhibited no such correlation. The jumbo-seeded trait has no taxonomic status, and it remains unclear whether it is ancestral or derived.